Carotenoid epoxide

Seventy naturally occurring carotenoid epoxides have been referenced and 43 of them have been fully characterized. These compounds can be formally considered oxidation products as defined above, but they first have the status of carotenoids. They are indeed found in vivo and are possibly biosynthesized from the corresponding non-oxidized carotenoids. If carotenoids containing epoxide functions have been found in humans, the epoxidation reaction has not yet been proven to occur in humans. 

Romer, S. et al.. Genetic engineering of a zeaxanthin-rich potato by antisense inactivation and co-suppression of carotenoid epoxidation, Metabol. Eng. 4, 263, 2002. 

Similarly, Karrer and oo-workers discovered that the carotenoid flower pigment trollixanthin (XV),103 as veil aa the related substances anthoroxsnthin, M, i4 violaxanthin, 1 and epoxylutein, 10-(1 all contain epoxide units. The. subject of naturally-occurring carotenoid epoxides ha been reviewed recently.1. 8 8 and attention called to the possible need for revision in certain of the structural assignments made by Karrer and hie associates.885... 

Mass Spectrometry. In an important and extensive survey, the mass spectrometric fragmentations of a wide range of carotenoids with specific deuterium labelling have been reported. On the basis of this work, the mechanisms of the well-known M—92, Af-106, Af-79, and Af-158 in-chain fragmentations, of some end-group fragmentations, and of the M— 80 and other fragmentations of carotenoid epoxides have been reassessed, and in several cases new mechanisms are proposed.38... 

Nybraaten, G., and S. Liaaen-Jensen New carotenoid epoxides from Trentepohlia iolithus. Acta Chem. Scand. B 28,483 (1974). 

Carotenoid epoxides are among the most widespread vegetal pigments. An example is zeaxanthine-diepoxide (Fig. 6) (Karrer, 1948). These... 

Little is known about the biological significance of carotenoid epoxides. Karrer suggests that they might function as oxygen carriers. This question merits further attention. 

The AE reactions on 2,5,5-trisubstituted allyl alcohols have received little attention, due in part the limited utility of the product epoxides. Selective ring opening of tetrasubstituted epoxides are difficult to achieve. Epoxide 39 was prepared using stoichiometric AE conditions and were subsequently elaborated to Darvon alcohol. Epoxides 40 and 41 were both prepared in good selectivity and subsequently utilized in the preparation of (-)-cuparene and the polyfunctoinal carotenoid peridinin, respectively. Scheme 1.6.12... 

The speed of autoxidation was compared for different carotenoids in an aqueous model system in which the carotenoids were adsorbed onto a C-18 solid phase and exposed to a continnons flow of water saturated with oxygen at 30°C. Major products of P-carotene were identified as (Z)-isomers, 13-(Z), 9-(Z), and a di-(Z) isomer cleavage prodncts were P-apo-13-carotenone and p-apo-14 -carotenal, and also P-carotene 5,8-epoxide and P-carotene 5,8-endoperoxide. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates lycopene > P-cryptoxanthin > (E)-P-carotene > 9-(Z)-p-carotene. 

There are few naturally occurring oxidation products that do not belong to the families of epoxides or apo-carotenoids. One of those is the metabolite of lycopene known as 2,6-cyclo-lycopene-1,5 diol found in human plasma and at lower levels in tomato products. ... 

In the second oxidation method, a metalloporphyrin was used to catalyze the carotenoid oxidation by molecular oxygen. Our focus was on the experimental modeling of the eccentric cleavage of carotenoids. We used ruthenium porphyrins as models of cytochrome P450 enzymes for the oxidation studies on lycopene and P-carotene. Ruthenium tetraphenylporphyrin catalyzed lycopene oxidation by molecular oxygen, producing (Z)-isomers, epoxides, apo-lycopenals, and apo-lycopenones. 

It must be underlined that independently of the MS equipment characteristics, no information about stereo-chemistry can be obtained. In fact, cis and trans isomers of the corresponding carotenoid showed identical mass spectra, as did carotenoids with epoxide groups at 5,6 and 5,8 positions. In addition, special care should be taken in assigning carotenoid molecular masses to avoid confusion due to the various ions that may be formed depending on measurement conditions. 

Britton, G., UV/visible spectroscopy, in Carotenoids Spectroscopy, IB, Britton, G., Liaaen-Jensen, S., and Pfander, H., Eds., Birkhanser, Basel, 1995, 13. Melendez-Martinez, A.J. et ah. Identification of isolntein (Intein epoxide) as cis-antheraxanthin in orange juice, J. Agric. Food Chem., 53, 9369, 2005. 

In order to obtain nearly absolute purity of the spectra of these xanthophylls, it was necessary to calculate the difference Raman spectra. Therefore, for zeaxanthin, two spectra of samples, one containing violaxanthin and the other enriched in zeaxanthin, were measured at 514.5 nm excitation. After their normalization using chlorophyll a bands at 1354 or 1389 cm-1, a deepoxidized-minus-epoxidized difference spectrum has for the first time been calculated to produce a pure resonance Raman spectrum of zeaxanthin in vivo (Figure 7.10b). A similar procedure was used for the calculation of the pure spectrum for violaxanthin. The only difference is that the 488.0nm excitation wavelength and epoxidized-minus-deepoxidized order of spectra have been applied in the calculation. The spectra produced using this approach have remarkable similarity to the spectra of xanthophyll cycle carotenoids in pure solvents (Ruban et al., 2001). The v, peaks of violaxanthin and zeaxanthin spectra are 7 cm 1 apart and in correspondence to the maxima of this band for isolated zeaxanthin and violaxanthin, respectively. The v3 band for zeaxanthin is positioned at 1003 cm-1, while the one for violaxanthin is upshifted toward 1006 cm-1. 

Absorption and Raman analysis of LHCII complexes from xanthophyll biosynthesis mutants and plants containing unusual carotenoids (e.g., lactucoxanthin and lutein-epoxide) should also be interesting, since the role of these pigments and their binding properties are unknown. Understanding the specificity of binding can help to understand the reasons for xanthophyll variety in photosynthetic antennae and aid in the discovery of yet unknown functions for these molecules. 

The interaction of carotenoids with cigarette smoke has become a subject of interest since the results of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group 1994 (ATBC) and CARET (Omenn et al. 1996) studies were released. P-Carotene has been hypothesized to promote lung carcinogenesis by acting as a prooxidant in the smoke-exposed lung. Thus, the autoxidation of P-carotene in the presence of cigarette smoke was studied in model systems (toluene) (Baker et al. 1999). The major product was identified as 4-nitro-P-carotene, but apocarotenals and P-carotene epoxides were also encountered. 

The oxidation of P-carotene with potassium permanganate was described in a dichloromethane/ water reaction mixture (Rodriguez and Rodriguez-Amaya 2007). After 12 h, 20% of the carotenoid was still present. The products of the reaction were identified as apocarotenals (apo-8 - to apo-15-carotenal = retinal), semi-P-carotenone, monoepoxides, and hydroxy-p-carotene-5,8-epoxide. 

The HPLC analysis of milkweed, the food-plant source for Monarch butterflies, demonstrates that it contains a complex mixture of carotenoids including lutein, several other xanthophylls, xanthophyll epoxides, and (3-carotene, Figure 25.3b. There is a component in the leaf extract that is observed to elute near 8min, which has a typical carotenoid spectrum but is not identical to that of the lutein metabolite observed at near the same retention time in the extracts from larval tissue. 

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